Field of the Invention:
The invention relates to a turbocharger having an insertion plate on the compressor casing.
In general, a turbocharger has an exhaust gas turbine which is arranged in an exhaust gas flow and is connected by way of a shaft with a compressor in the intake tract. During operation, the exhaust gas flow is directed into the turbine where it drives the latter's turbine wheel. The turbine wheel in turn drives the compressor wheel, by means of which the compressor increases the pressure in the intake tract of the engine. During the induction cycle, a greater quantity of air therefore enters the cylinder. The result of this is that more oxygen is available and a correspondingly greater quantity of fuel can be combusted. This means that the power output of the engine can be increased.
In the case of turbochargers having a radial compressor, the air is first accelerated through the compressor rotor and kinetic energy is added to the gas. In a following radial diffuser, tangential and radial speed components are delayed and the required static pressure is thus built up. The characteristic external diameter of such a radial diffuser is normally 1.5 to 1.7 times that of the radial opening diameter. Connected to the diffuser is a so-called spiral which accepts the compressed gas and delivers it to the engine. In this situation, the compression ratio of the radial compressor depends in a first approximation on its rotational speed. With different engine mass flows and compressor circumferential speeds, a compressor wheel exit angle of the flow in a range from 30° to 80° results. Depending on the design of the spiral, in other words of the surfaces with respect to the radius ratio, a minimum total pressure loss of the spiral results at an exit angle of 45° to 80°.
With regard to the construction of a spiral, a compromise often needs to be found between the installation space available in the engine compartment and the optimum geometry in terms of flow engineering. In general this results in so-called overhanging spirals. Overhanging spirals are characterized by a radius of the centroid of the cross sectional area, which is similar to the diffuser exit radius.
Overhanging spirals can only be manufactured in a casting process using a core. A die-casting process is rejected here on account of the tooling. In order to obtain the required diffuser exit radius for the pressure recovery it is therefore necessary to provide a large installation space for die-cast spirals or to accept a lower pressure recovery. Furthermore, die-cast spirals are characterized by a lower degree of efficiency. On the other hand, die-cast spirals offer a clear cost advantage compared with the permanent mold casting process for example.